Field of the Invention
The present invention relates to a tension type of a modular concrete form or forming structure and method of manufacture thereof. According to my invention, a new and improved curved concrete forming structure is herein disclosed. The structure includes arcuately curved form panels joined together in side-by-side relation as a gang for the formation of curved walls. More specifically, the invention concerns a concrete forming system whereby the panels can be pre-formed at a factory site, if desired, and then shipped to a customer's building site for erection and for the pouring of a curved concrete wall utilizing inside and outside concrete forms which are tied together. By forming the curved steel angles for my form panels at a factory location, it has been found that considerable time can be saved and resultant cost can be reduced because of the reduced amount of labor required to assemble or erect the concrete forming panel.
According to my invention the panels each include a pair of factory formed curved angles for top and bottom edges of each panel and the radii of the angles corresponds to the radii of the concrete wall to be poured. These angles are preferably assembled with steel plates in the factory to reduce cost, but angles having different radii can be interchanged in the field if desired while still avoiding the field problems of attempting to adjust curvatures by the techniques disclosed in U.S. Pat. No. 4,679,763.
According to other improved features of my concrete forming structure, my construction enables a steel skin plate to be flexed to form a desired arc whereby no chording effect will be produced in the poured concrete surface. Unlike convention panel systems that require grinding or rubbing out form joints, my curved concrete forming structure produces a smooth architectural surface that requires minimal finishing labor. My all-steel concrete forming structure provides all the strength and versatility needed even though its form face or skin plate is only 3/16" thick. The curved concrete forming structure has 4" deep vertical stiffners to provide a 1,000 psf system that handles any radius 5' or over, which far exceeds the capabilities of any other known curved concrete forming structure. The 1,000 psf concrete system enables concrete to be poured more quickly in contrast to prior art constructions.
According to important features of my invention pre-rolled steel ribs are used to set the radius of each curved form panel. The curved top and bottom ribs are rolled to a curved shape and serve to securely hold the form in a predetermined radius as required. When assembling the pre-rolled steel ribs with the skins, the skin plate is placed in a position facing the ground, and top and bottom ribs are bolted to vertical stiffners on the backside of the steel skin plate. The panels conform precisely to the radius of the ribs and no torque bolts are needed.
Should a given job require the pouring of walls with a different arc or tanks of a different radius, the builder can simply order extra sets of top and bottom ribs for the same forms.
The panels are adapted to be stacked by bolting the top and bottom ribs adjacent forms with 3/4" fit-up bolts and nuts so that the panels can be quickly assembled and disassembled after use.
Typically a form panel consists of a face material stiffeners (or cross-members; side rails (or ribs) and end rails (or end bars). To flex any of the known systems in order to achieve a radius, additional exterior structural elements are used i.e., adjustable curved walers, rolled channels or a tension strap.
According to my invention, a desired radius can be attained by first rolling one of the required panel components, the side rail (or rib) to the required radius. The assembly of the panel then produces a curved panel which is independent of exterior elements. To change curvature, the panel is disassembled and the rolled component is replaced with a like piece which has been pre-rolled to the new curvature. Re-assembly of the panel then produces a new radius which is structurally inherent in the panel once again.
In the past, other types of concrete forming systems have been used and one example is shown in U.S. Pat. No. 4,679,763 assigned to Economy Forms Corporation. In this patent the patentee discloses a metal form which is suited for pouring curved walls. The concrete form is actually formed to a desired curvature at the pour site. The actual curvature of the form is established at the pour site. The principle components of the form are sent in a flat form from the manufacturer to the builder and the builder then makes adjustments in the components of the form after the components have been assembled to establish a desired curvature in the form so that a concrete wall can be poured having a predetermined radius.
Other techniques for forming curved walls are taught in other existing U.S. Patents including U.S. Pat. No. 4,553,729 issued to Frank T. Connors. In this patent, the patentee uses a series of at least three vertically extending rows of concrete form panels which are joined together in side-by-side relation as a gang for use in the formation of straight or curved concrete walls. In this instance, each of the concrete form panels are of a so-called "straight" or "non-curved" construction. Where the radius of a wall is sufficiently large, and the length of the concrete form panels are a small increment of the curvature of the curved wall to be poured, the concrete form panels each function as a chord and co-act in the previously stated environment as a small increment in such a way as to enable a curved concrete wall to be formed. The patentee does not in this patent contemplate the use of curved concrete form panels that are pre-formed to shape in a factory location and then shipped to a job site for installation by a builder in the creation of curved concrete walls.